Personally I'd have no issues having it include concoctions such as Bane poisons or Monster Drool. Why not? They aren't hideously lethal, they're certainly appropriate to the ninja's idiom, and they're within the realm of what seems like a gizmo. Here is that list, also courtesy of Sir Pudding:

Otherwise, I'd go with GM rulings on individual items. After all, if the GM and player both think a given item really fits the term "Ninja Tool" and otherwise is covered by the gizmo rules, it should be covered. And certainly a GM is within his or her rights to veto anything from the list above! But it's a good starting point at the very list.

(Oh and don't forget, Ninja Tools lets you trick out your weaponspermanently. It's a powerful tradeoff for not having that one little piece of gear you really need . . .